As a method for measuring the electric-field distribution inside semiconductor device, such as semiconductor integrated circuits and semiconductor elements, in a non-destructive/non-contact manner, a terahertz (THz) electromagnetic-wave imaging method using laser has been known (KIWA Toshihiko and TONOUCHI Masayoshi, “Back-scattered Terahertz Imaging for Fault Isolation in Integrated Circuits,” Japan Society of Applied Physics, Springtime Academic Lecture Meeting, Extended Abstracts, the Third Volume, p. 1,183, (Mar. 29, 2003)). This is one in which a THz electromagnetic wave is generated by irradiating a laser beam onto a circuit surface after applying a voltage to the circuit of a semiconductor device and the electric-field strength at the laser irradiation position is measured from the amplitude intensity of the generated electromagnetic wave. However, since this conventional method makes use of the amplitude intensity of the generated electromagnetic wave alone, the difference between the electric-field directions cannot be distinguished and the obtained information is less so that it is insufficient for the inspection or failure diagnosis for semiconductor device. Moreover, the spatial resolution of measurement is prescribed by the diffraction limit of irradiating laser beam, and accordingly there is a problem in view of resolution in order to measure the electric-field distribution of fine semiconductor integrated circuit. Further, the conventional method can measure the electric-field distribution of entire circuit only, and cannot measure the electric-field distribution of specific region, such as the signal channel alone, for instance.
Moreover, as a technique which is related to the aforementioned prior art, a technique (FIG. 1) has been known, technique in which an ultra-short optical pulse is irradiated onto a semiconductor switch to radiate a terahertz electromagnetic wave into air (D. H. Auston and M. C. Nuss, “ELECTROOPTIC GENERATION AND DETECTION OF FEMTOSECOND ELECTRICAL TRANSIENTS,” IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol. 24, pp. 184-197, FEBRUARY 1988.). In FIG. 1, a low-temperature grown (LT) GaAs thin film, which works as a photoconduction film, is grown on a semi-insulative GaAs substrate, and further antenna structures, which are disposed at intervals of 5 μm approximately, are made on it with a gold alloy. In general, an LT-GaAs has been used as a photoconducting thin film in which an electric current flows in an instant only when an optical pulse is irradiated. The gold-alloy portions double as electrodes, and are connected with a direct-current voltage source. The central projections act as a micro dipole antenna, and, when a pulse laser beam is emitted to this gap portion to excite it, the carrier is excited from the valence band to the conduction band by means of light absorption, and the excited carrier relaxes after it is accelerated by the applied voltage. When considering this movement of the carrier an instant electric current, a pulse electromagnetic wave, which is in proportion to the time derivative of this electric current, generates.
As aforementioned, in the prior art, there are such problems that the direction of electric field cannot be distinguished, the spatial resolution of electric-field distribution measurement is low, and the electric-field distribution of specific region cannot be measured.
The present invention is one which has been created anew in order to solve such problematic points. That is, the object of the present invention is to provide an electric-field distribution measurement method and apparatus, which can distinguish the direction of electric field, whose spatial resolution is high, and which can measure the electric field in specific region.